Heat oil in a large skillet over medium high heat. Add onion and cook until slightly softened. Add garlic, lamb, and pork and continue to cook, breaking meat apart with a spoon, until meat is browned. Drain any excess fat and return to the pan. Add ricotta and mascarpone cheeses and stir until melted into the meat. Add marinara sauce and heat until just simmering. Add pasta to the sauce and cook for 1-2 minutes together for pasta to absorb the sauce. Season with salt and pepper to taste. Either stir mint into paste or sprinkle over the top as a garnish.